Hello,
testpos@srap53dxr1:~> psql --help
...
-d, --dbname=DBNAME database name to connect to (default: "testpos")
testpos@srap53dxr1:~> whoami
testpos
testpos@srap53dxr1:~> env | grep PG
PGPASSWORD=xxxxxxxx
PGHOST=localhost
PGPORT=5432
testpos@srap53dxr1:~> LANG=C psql -Usisis
psql (13.3)
Type "help" for help.
sisis=# \l
List of databases
Name | Owner | Encoding | Collate | Ctype | Access privileges
-----------+----------+----------+-------------+-------------+-----------------------
postgres | postgres | UTF8 | de_DE.UTF-8 | de_DE.UTF-8 |
sisis | sisis | UTF8 | de_DE.UTF-8 | de_DE.UTF-8 |
...
Why psql connects to the database 'sisis'? I was expecting that it
will try to connect to a database 'testpos' as this is the UNIX login
and as '-d....' was not specified. I was expecting in this case an
error like this:
testpos@srap53dxr1:~> export PGDATABASE=testpos
testpos@srap53dxr1:~> psql -Usisis
psql: error: FATAL: database »testpos« does not exist
What do I uderstand wrong?
When you try to connect without specifying a database name on the command line, psql will check PGDATABASE. If unset, it will use the PostgreSQL user name also as the database name. If you don't specify explicitly the PostgreSQL username, it will check PGUSER and, if unset, will use the OS username.
That matches all your examples above.
--
Guillaume.